Iphone 4s and the Samsung Galaxy are both great, and you'll probably be happy with both.
If you want a slightly more polished experience, want most stuff to work all the time, and don't care too much about customization, get the iPhone. If you want total control, but are willing to accept the occasional bugs and glitches that go along with an open sourced platform like Android, get the Galaxy.
Or dump sprint, get on Verizon, and decide between the iPhone and the Nexus. Just be willing to deal with battery issues that a 4.6 inch 4G phone will have until they make a better battery.